In the tires for small trucks or the like, and tires for four-wheel drive vehicles designed to run off the road in the muddy or sandy field such as Jeeps, they are often used at low internal pressure in order to maintain stability of traveling and comfort of riding. Such tires for small trucks tend to have low aspect ratio as the load increases. Or four-wheel drive vehicles running in the muddy or sandy fields are promoted in this tendency in order to improve the floating performance.
As a result of increasing the ground contact surface by employing this low aspect ratio, however, the ground contact pressure is decreased. Further, the belt layer is repeatedly subjected to bending deformation in the tire radial direction in traveling, so that breakage in the circumferential direction known as buckling is often caused in the end portion of the belt layer or near the groove bottom.
Usually, in the tires for small trucks and four-wheel drive vehicles, in order to decrease the deformation of the belt layer, the center part of the tread is formed in a greater thickness than the tread shoulder part. And therefore in the tires subjected to heavy load as used in Jeeps or the like, the rubber thickness is abnormally large in the center part, and the tire weight increases, and the cost also soars.
It has been hence required to have the tire constitution capable of protecting the belt layer from damage without abnormally increasing the thickness of the rubber in the tread part.